Controlling fuel supply to multizone heating furnaces



Sept. 26, 1950 F. s. BLOOM 2,523,644

CONTROLLING FUEL SUPPLY T0 MULTIZONE HEATING FURNACES I Filed Sept. 4, 1946 soo- D/Is'efiar e Fin hem fol-e Szeel Elli nerd fare INVENTOR FREDERICK S. BLOOM Patented Sept. 26, 1950 CONTROLLING FUEL SUPPLY TO MULTI- ZONE HEATING FURNACES Frederick s. Bloom, Pittsburgh, Ba.

Application September 4, 1946, Serial No. 694,734

1 This invention relates-to controlling the fuel supply to multi-zone heating furnaces. It has to do with the control of the fuel supply to furnaces for heating material, as, for example,v billets, slabs, shapes, etc.,.,and which furnaces have a plurality of heating zones.

-The invention will for purposes of explanation and illustration be described as embodied and practiced in apparatus for and a method of supplying fuel to a heating furnace for heating steel billets. The invention is=not limited to employment in connection with the heating of steel or of billets but'is perhaps most commonly embodied and practiced in apparatus for and a method of controlling the fuel supply to multizone heating furnaces for heating steel billets. The furnace which has been selected for illustrative purposes is an elongated-furnace of the pusher type through which steel billets are moved substantially horizontally and in a straight line from the entranceend to. the discharge end of the furnace. the furnace-having a heating zone below the path of the billets and relatively near the entrance endofthe-furnace and another heating zone abovethe path of the billets and relatively near the dischargeend of the furnace.

In the operation of multi-zone heating furnaces it is customary to introduce heat continuously in the various zones. Various methods of control have been attempted but multi-zone heating furnaces as heretofore operated have not hadthe efficiency desired. I have discovered how to greatly increase the efficiency of multi-zone heating furnaces and at the same time improve the quality of the material heated, i. e., in the illustrativeeiiample, steel billets.

8 Claims. (of. 263-43) supply is about 40% of the maximum rated capacity of the burner means at the second zone.

ably about doubling it.

I provide, in the supplying of fuel to a multizone heating furnace, the steps of supplying fuel at one zone at a rate sufficient to maintain a predetermined temperature at a selected point up to a predetermined rate and when the rate of supply of fuel at said zone attains said predetermined rate and more fuel is required to maintain said temperature at said point increasing the rate of supply of fuel at said zone and simultaneously supplying additional fuel at another zone at a rate bearing a predetermined relationship to the rate of supply of fuel at the first mentioned zone and such that the fuel supplied at the first mentioned zone and that supplied at the second mentioned zone together maintain said temperature at said point.-' Preferably the temperature used for control is the discharge temperature, either the'furnace temperature at point of material discharge or. the temperature of the work as it is discharged from the furnace. Preferably I supply fuel at one zone sufficient to maintain a predetermined material discharge temperature up-to a rate about 40% of the maximum rated capac- I have found that in operation of a heating furnace having a heating zone below the path of the material and relatively close to the entrance end of the: furnace and anotherheating zone above the path of the material and relatively close to the discharge end of the furnace a great deal of heat is wasted in the first mentioned zone. I find that remarkable efiiciency and saving of fuel can be obtained and a product of improved quality produced if when the furnace is operated at low capacity the heat is introduced entirely or substantially entirely in the second zone and when the'furnaceis operated at progressively increasing capacities heat is added in the first zone andfor higher capacities the heat input in the first zone is increased at a faster rate than the rate of increase of heat input in the second zone. I' prefer "to supply heat en- 'tir'ely in-the second" zone until the rate of fuel ity of the burner means at said zone and when the rate of supply of fuel at said zone attains about 40% of the maximum rated capacity of the burner means at said zone and more fuel is required to maintain the predetermined discharge temperature I increase the rate of supply of fuel at said zone andsimultaneously supply additional fuel at anotherzone at a rate bearing a predetermined relationship to the rate of supply of fuel at -the first mentioned zone and such that the fuel supplied at the first mentioned and that supplied: at the second mentioned zone together maintain the dischargetemperature. While the predetermined relationship between the two rates ofssupplying fuel may vary depending on condi tions, I preferably increase the rate of supplying fuel at the second-mentioned zone faster than I increase the rate of supplying fuel at the first mentioned zone. Desirably, I increase the rate of supplying fuel at the second-mentioned zone twice as fast as I increase the rate of supplying v.ature at said point.

fuel at the first mentioned zone. The aggregate fuel supply should be such as to maintain the desired discharge temperature.

I further provide fuel supply apparatus for supplying fuel to a multi-zone heating furnace comprisin a source of fuel, burner means respectively at a plurality of zones in the furnace, connections from the source of fuel to the burner means at the respective zones, a controller responsive to the temperature at a selected point in the furnace and controlling the flow of fuel to the furner means at one zone at a rate sufficient to maintain a predetermined temperature at said point up to a predetermined rate, a ratio regulator responsive to. the flow-of fuel to the burner means at said zone regulating flow of fuel to theburner meansat-another zone so that when the rate of flow of fuel to the burner means at the first mentioned zone attains said predetermined rate and more fuel .is required to maintain said temperature at said point further'increase .of the rate of flow of fuel to the burner means at the first mentioned zone causes flow of fuel to the burner means at the second mentioned zone at a rate bearing a predetermined relationship to the rate of flow of .fuel to the burner means at the first mentioned zone and such that the fuel supplied at the first mentioned zone and that supplied at the second mentioned zone together maintain said temper- The controller may control a valve in the fuel line leading to the burner means at one zone and the ratio regulator may ,be responsive either to the fuel flow moving to the first mentioned zone or to the position of the valve controlling the flow of fuel to the first mentioned zone and regulates the fuel flowing to the burner means at the second mentioned .zone.

longitudinal cross-sectional view through a furnace for heating steel billets;

Figure 2 is a curve in which steel temperature is plotted against position in furnace showing the manner in'which steel billets ma be heated according to my invention in the furnace of Figure 1; and

Figure 3 is a diagram-ofapparatus which may be employed for'control of the flow' of fuel to the burner means at the respective zones of the furnace.

Referring now more particularly to Figure 1, the furnace may be conventional, comprising means forming an elongated enclosure 2 through which shapes 3 are adapted to be moved generally horizontally in a straight line. Ordinarily the shapes are pushed through the furnace in the direction from right to left viewing Figure 1.

The means for supporting and pushing the work through the furnace may be conventional and'hence are not shown. The work passes first through a preheating zone 4, then through a heating zone 5 and finally through a heating -rzone6. The work is preheated'in the zone 4, is further heatediin the zone '5 where heat may be :applied to the Work from beneathand isfinally heated to discharge temperature in the zone 6 where heat is applied from above. The burners are shown at 1 and 8, respectively, and are introduced through burner openings I and 8 for heating the zones 5 and 6 respectively. As each billet reaches the incline 9 it slides down that incline to a roller table I0 on which it is delivered to the rolling mill or other processing apparatus.

A temperature controller has a heat sensitive portion ll disposed in the zone 6 so as to be re- :sponsive to the temperature in that zone. The controller may be responsive to the temperature cfthe-atmospherefin zone 6 or to the temperature of the heated work, depending upon its precise positioning. -.The controller may be conventional, being designated l2 in Figure 3 and operating through a relay 13 a motor I4 and linkage l5 to turna butterfly valve IS in a fuel conduit I! leading from a main fuel supply conduit I8. The fuel conduit l1 leads to the burners B in zone 6.

The temperature controller I2 is set for a predetermined temperature. If the temperature in zone 6 falls *below the temperature for which the controller I2 is set the controller operates in normal manner to open valve'lfi and admit more fuel to the burners 8' wherebythe temperature in zone 6 is increased. If the temperature rises slightly above the temperature for which the controller I2 is set the controller operates in its usual way to'turn the-valve I6 toward closed position, reducing the rate of flow of fuel to the .burners 8 and hence lowering the temperature in zone 6.

'When thefurnace is operated at low capacity I apply heat only by operation of the burnerst. The burners *1 operating through the burner openings *1 are not employed when the furnace is operating .at low capacity. I find that when the burners'B are operated at'a rate not greatly exceeding about 40% of the maximum rated capacity thereof most efficient results are obtained by using only theiburners 8 and not intro- .ducing .heat elsewherein the furnace. When, howeventhe rate ofdelivery of fuel to the burners 8 substantially exceeds .about 40% of the maxi- .mum ,rated capacity .of such burners it is desirablelto addheatinzone'fi. Fuel is delivered to thelburnersnltlirough .a conduit ,2! communieating .with the;main'fuel supply conduit 18. A valve 2-2--controls the .flow .of .fuel .through' the conduit 2|; The .valve 22 .is operated by a ratio regulator indicateddiagrammatically in Figure 3 and designated. generally by reference numeral 23. Any conventional ratio regulator may be employed, as, for example, :an Askania ratio regulator equipped with a conventional bias spring. The regulator is responsive to-the rate of fuel flow through the .conduit I1 and operates the -valve -22 to-control the rate of fuel flow through the conduit 2| so that'the rates of fuel fiow through theconduits I! and 2! have a predeterminedrelationship to each other. Desirably the regulator maintains the valve .22 closed .untilthe rateuof .fuel flow through the conduit H is such that :the fuel delivery therethrough exceeds about 40% of the maximum rated capacity of-the burners .8. When the fuel fiow throughthe conduit l1 exceeds about 40% .of .the maximum rated capacity vof the burners 8 and more fuel .is required to maintain the predetermined discharge temperature for .which the controller 12 .is set I increase the ,rate of; supply of .-fuel through-the :conduit l1 and-also simul- .taneously through the regulator 23 causing opening of the valve 22 to supply additional perature furnace when my control system is employed.

add heat in the zone 5'. I find it desirable to increase the rate of feed of fuel to the burners 1 faster than I increase the rate of feed of fuel to the burners 8 after the valve 22 begins to open;

that is to say, after the rate of feed of fuel through the conduit ll substantially exceeds about 40% of the maximum rated capacity of the burners 8. While the relationship between the rate of feed of fuel through the conduit I1 and the rate of feed of fuel through the conduit 2| may vary substantially depending on conditions I find that generally speaking excellent results are obtained when the rate of supply of fuel at the zone 5 is increased twice as fast as the rate of supply of fuel at the zone 6. When both the burners 8 and the burners l are being employed simultaneously they cooperatively maintain the desired discharge temperature.

The curve of Figure 2 shows how steel temincreases with travel through the The highest temperature is the discharge temperature which is used for control purposes. I

can save 25% or more of the amount of fuel 7 which is used in similar furnaces not equipped with my control mechanism as commonly operated by those skilled in the art. It is to be understood that by manual adjustment of the ratio regulator slider various relationships between rate of fuel flow to the burners 8 and rate of fuel flow to the burners I may-be obtained. The equipment employed may vary widely. The regulator may operate from the fuel flow itself in the conduit I! or it may operate from the valve l6 or the handle thereof, as the position of the valve is an index of fiow volume.

Valve 22 can be controlled by electric, hydraulic or pneumatic devices as may be desired in any particular instance.

I .While I have shown and described a present ...preferred embodiment of the invention and have illustrated a present preferred method of. prac- .ticing the same, it is to be distinctly understood II that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.

I claim: r v

i. In the supplying of fuel to a heating furnace through which. material to be heated is adapted to pass and which has a first heating zone relatively near the material inlet and a second heating zone relatively near the material outlet, the steps of supplying fuel at the second zone. at a rate suffilcient to maintain a predetermined discharge temperature up to a predetermined, rate and when the rate of supply of, fuel at the second zone attains said predetermined rate and more fuel is required 'to maintain said discharge temperature increasing the rate of supply of fuel at the second zone and simultaneously supplying additional fuel at the first zone at a rate bearing a predetermined relationship to the rate the second zone at a rate suflicient to maintain a predetermined discharge temperature up to a predetermined rate and when the rate of supply of fuel at the second zone attains said predetermined rate and more fuel is required to maintain said discharge temperature increasing the rate of supply of fuel at the second zone and simultaneously supplying additional fuel at the first zone at a rate bearing a predetermined relationship to the rate of supply of fuel at the second zone and such that the fuel supplied at the first zone and that supplied at the second zone together maintain said discharge temperature.

3 In the supplying of fuel to a heating furnace through which material to be heated is adapted to pass generally horizontally in a straight line and which has a first heating zone below the path of the material and relatively near the material inlet and a second heating zone above the path of the material and relatively near the material outlet, the steps of supplying fuel at the second zone at a rate suflicient to maintain a predetermined discharge temperature up to a rate about 40% of the maximum rated capacity of the burner means at the second zone and when the rate of supply of fuel at the second zone attains about 40% of the maximum rated capacity of the burner means at the second zone and more fuel is required to maintain said discharge temperature increasing the rate of supply of fuel at the second zone and simultaneously supplying additional fuel at the first zone at a rate bearing a predetermined relationship to the rate of supply of fuel at the second zone and such that the fuel nace through which material to be heated is adapted to pass generally horizontally in a I straight line and which has a first heating zone below' the path of the material and relatively near the material inlet and a second heating zone above the path of the material and relatively near the material outlet, the steps of supplying fuel at the second zone at a rate sufficient to maintain a predetermined discharge temperature'up to a "rate about 40% of the maximum rated capacity of'the burner means at the second zoneand when the rate of supply of fuel at the second zone attains about 40% of the maximum rated capacity of the burner means at the second zone and more fuel is required to maintain said discharge temperature increasing the rate of supply of fuel atthesecond zone and simultaneously supplying additional fuel at the first zone ata predetermined rate, and increasing the rate of supply of fuel. at the first zone faster than at the second zone, the aggregate fuel supply being such as to maintain said discharge temperature. v

5. Fuel supply apparatus for supplying fuel to a heating furnace through which material to be fuel to the burner means at the second zone at a rate sufficient to maintain a predetermined discharge temperature up to a predetermined rate,

a ratio regulator responsive to the flow of fuel to -the burner means at the second zone regulatin flow of fuelgto the-burnermeans at-thefirst zone so that when the rate of flow :of fuel :to the burner ;means at the second zone attains said predetermined rate and moreifuel is required to ;maintain said predetermined discharge temperature further increase of the rate of flow offuel -:;to the burner means at the second zone causes -flow of 'fuelito the burner means at the firstizone at a rate-bearinga predetermined relationship to -the,rate of fiow of fuel'to theburner means at the-second zone and. such that the fuel supplied at the first zone and that supplied at thesecond zone together maintain said predetermined .dischargegtemperature.

6- ;;Euel supply apparatus for-s pplyin f ellto ;a heating f-urnace through which material to-be lheated isadapted to pass generally horizontally :ina. straight line. and which has alirst heating "zqnepelow'thepath10f the materialand relativelv-near'the material inlet and alsecondoheat- ,ing zone; above'the path of-the material and relatively near the material outlet comprising a 35011106- ofifuel, burner meansat each of said zones, .-connec,tionsrfrom the souroeof fuel to the burner means at the respective zones, a controller responsive-to the-discharge temperature and controlling thefiow-of' fuel to the burner .means at thesecondzoneat a ratesuificient to maintain a predetermined discharge temperatureup to a; predetermined rate,,-a ratio regulator responsive to the: flow: of fuel to-the burner means at-theseeond -:z one regulating flow 7 of fueltto ;the burner ;means -at-;the first;zoneso that when the rate ,of flow of; fuel to :the burner means at the-second zone attainssaid predeterminedrate and moreyfuel is required to maintain said predetermined discharge temperature further increase-of the rate 9Qf1flGW-1Qifl161 to thezburner :means. at the second 3ZOI1 causes flow of =fuel to. the burner means at-the -first ;z one at a rate bearing a predetermined-relationship to the rate of flow of. fuelrto the burnermeansatlthe second zone andsuch lthatthe fuel supplied at'athefirst zone and that supplied at the second zone together maintain said predetermined discharge temperature.

J7, Euel supply apparatus for supplying ,fuel .to .azheating furnace throughwhich material to be heated is adaptedto pass generally horizontally inz,,a;straight lineand which has afirstheatingj -zone below the path of the material. and re1aitivelyi near the material inlet and-a second-theating: zone .above the path of the material and relatively near the material outlet comprising-a :esource of.-fuel, burner meansineach of said zones,

-,connectionsjfromthesource of fuel to theburner a predetermineddischarge temperature .up toa rate about 40% ,of the maximum rated capacity .of the burner ,means at the second zone" aratio regulator responsive to the flow of fuel to .the

burner, means: at, the 1 second zone; regulating mfiow of fuel to the burner means at the first zone. so thatwhen therateof flow of fuel tothe burner gmeans at the second zone attains about 40% ref the maximum'ratedcapacity of the burner means at the secondzoneand more fuel is required (to maintain said predetermined discharge tempera- ,turefurther increase of the rate of flow offuel .to theburner meansat the second zone causes flow of. fuel to the burner means at the first zone ;at a rate bearing o, predetermined relationship to the ,rateof flow of fuel to the burner means at the secondzone and such that thefuelsupplied at the first zone and thatsupplied at the second zone together maintain said predetermined discharge temperature.

;8. Fuel supply apparatus for supplying ,fuel to aheating furnace through which material to be heated -is adaptedto pass generally-horizontally in a straight line and which has a first heating zonebelow the path of the material and relatively near the materialinlet and a second heatingzone above the path ofthematerial and relatively near the material outlet comprising a source of fuel, burner means in each of said zones connections from the sourceof fuel to the burner means at the respective zones, a controller responsive to the discharge temperature and controlling the flow of fuelto the burner means at the second zone at a rate sufficient to maintain a predetermined discharge temperature up to arateabout 40%,01? the maximumrated capacityof the burner meansat the second zone, a ,ratioregulatorrltesponsive to the flow of fuel to .the burnermeans at the seoondzone regulating flow of fuel ,to the burner means at the first zone so that when the rate offlow of fueltto the burner means at the second zone attains about 40% ,of the maximum ratedcapacity of .the burner meansat the second zone and more fuel is required to maintain said predetermined discharge temperature further increase of the rate of flow of fuel to the burner means at the second zone causes flow of fueltothe burner means at the first zone at substantially a predetermined rate, the aggregate fuelsupply being such as to maintain said predetermined discharge temperature.

FREDERICK s. BLOOM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,912,933 Culbertson June 6,1933 1,944,729 Charlesworth Jan. 23, 1934 2,133,673 Spencer et al. Oct. 18, 1938 2,246,550 Stewart et a1 June 24, 1941 2,298,149 Morton Oct. 6, 1942 2,362,045 Bliss Nov. '7, 1944 2,390,806 Nagel Dec. 11, 1945 2,451,349 Morton Oct. 12, 1948 

